In the 1930's, the first attempts to provide dental implants were unpredictable partially because of the materials which were used, and partially because of poor technique. The earliest implants were not capable of withstanding the loads provided thereto by chewing, the tongue and so forth.
During the 1960's and 1970's, the designs, materials and techniques utilized were radically altered and predictably acceptable results began to be achieved. The basic philosophy became to ensure that the implant was rigidly in place, with no capability for relative motion between it and the bony host. To ensure rigid securance of the implants, great care is taken to avoid any degradation of the immediately surrounding bone in preparing the site for the implant. Originally, the holes in the bones were tapped to provide an identical fit to screw threads on the implants; and in order to avoid excessive heat, low speed, high torque drills were used with cooling fluids. Implants are made of pure titanium or titanium alloys which are compatible with bone, fixtures, tools, and the ultimate prosthesis, as well as being innocuous in use over time. A sterile field was attempted to be maintained at all times.
Since then, many more improvements have been made in the materials, the parts, and the techniques. By way of example, a procedure which is widely practiced currently, illustrated in FIG. 1, utilizes a kit, contained in a sterile package, that includes a self-tapping implant 14, an insertion tool 15, held to the implant by a screw 16, and a carrier 17. The implant has threads 20, a self-tapping cutting edge 21, a recess 22, formed with the edge 21, which may have a hole 23 leading to a similar recess on the opposite side. The recess provides a place for the bone debris that forms from cutting the threads, thereby avoiding packing of the debris between the implant and the surrounding bone. The center of an outer end 24 of the implant is hollow and threaded (not shown) to receive the threads 25 of the screw 16. The outer end 24 also has a shallow hexagonal land 26 thereon for aligning the ultimate prosthesis (or abutment) therewith and for screwing the implant into the hole drilled into the bone. The land 26 is engaged by a hexagonal socket 28 formed in the insertion tool 15. The upper third (or so) of the insertion tool 16 has a hexagonal surface 30 which is engaged, initially by a hexagonal socket 33 formed in the carrier 17; the carrier may have serrations 34, or other features, to assist in handling it.
As shipped in a sterile bottle or other sterile package, the tool 15 is tightly secured over the land 26 by the screw 16, and the carrier 17 surrounds the hex surface 30 of the tool. The carrier typically forms the stopper of an interior bottle in a double sterile package. The implant may thus be hand started into the hole in the bone by means of the carrier. The carrier can then be shaken loose and removed. A socket wrench is then used to seat the implant subgingivally into the bone. Thus the process of securing the implant to the bone is readily achieved, with the sterility of all but the wrench ensured by packaging.
Once the implant 14 is properly secured in its final position, a hexagonal wrench is used to engage a hexagonal socket 36 formed in the outer end 37 of the screw, the screw 16 is backed out of the implant, and the insertion tool 15 is removed. Next, a healing screw 38 (FIG. 2) is threaded tightly into the implant to keep the outer end 24, the land 26 and the internal threads of the implant all clean and clear, as the gum tissue is allowed to heal over the healing screw. The healing screw 38 has a hex socket in its head 39 (not shown, similar to that of the screw 16) to permit rotating it with a hex wrench. The head 39 has an annular void to fit over, but not engage, the hexagonal land 26 on the implant 14.
This procedure requires that, after the implant is secured into the bone, the gum tissue covering the implant and healing screw thoroughly heal. For implants in the mandible, healing requires about three months; in the maxilla, about six months.
After healing, the gum is reopened, the healing screw 38 is removed, and an impression transfer pin 40 (FIG. 3) is secured to the implant 15 by a screw 41. The screw 41 may be rotated with a friction drive wrench. The transfer pin 40 is fit tightly to the implant 15 and x-rayed to ensure that it is tight and well mated, with no voids. Then, an impression is taken of the patient's mouth with the transfer pin in place. After the impression is completed, the screw and transfer pin are removed and a healing abutment (not shown) is threaded into the implant; the healing abutment typically extends above the gum line, so that the gum tissue can reheal, leaving an orifice open to the implant for later insertion of a suitable abutment which mounts the prosthesis.
While the second healing takes place, a laboratory prepares a working model of the mouth from the impression, utilizing the transfer pins, imbedded in the impression, to seat implant analogs (or dies) to which the prosthesis may be secured on the working model. Then the lab prepares the prosthesis, with the abutments which will be utilized for anchoring the prosthesis on the implants, secured to the implant analogs.
This process is long and cumbersome and has less than complete predictability, is traumatic for the patient, and difficult. In addition, maintaining sterility while manipulating all the small parts involved is a chore in itself. Furthermore, it is not uncommon for some of the small pieces to actually become lost (even down the throat of the patient). Visibility of the implant may be limited by blood and tissue.
In the process described above, the transfer pin is typically not provided in the sterile kit. As a consequence, there is a general practice of using the transfer pins over and over again. The transfer pins can become nicked and may have bits of material adherent thereto which together provide irregularities in the surface that impede both the seating of the transfer pin securely to the implant, without voids, prior to making the impression, as well as interfering with a faithful return to the impression when the construction is commenced. Furthermore, the seating of a transfer pin on an implant in a freshly prepared site is very likely to be less than perfect, with tissue or other debris lodging between the transfer pin and the implant; it is very unlikely that a debris-impeded fit would be replicated upon mounting an abutment for the prosthesis to the implant at the conclusion of the procedure.
In some cases, single stage implants, with abutments integrally formed thereon, have been used in a procedure which takes the impression on the mouth immediately after installing the implants. This procedure has not had general acceptance because it must be executed with extreme skill and without any significant anatomical contra indications or procedural mishaps. The temporization (protection) of the abutments through the tissue is also difficult. In contrast, the two stage process (hereinbefore) permits compensating for any incorrect angles or other misplacements of the implants. Furthermore, the abutment ends of the integrally formed implants are protected from tongue and chewing pressures for months, to avoid faulty healing. This requires easily adapting an existing denture or providing a temporary prosthesis, to cover the implants during healing.